1 """Generic interface to all dbm clones. 2 3 Use 4 5 import dbm 6 d = dbm.open(file, 'w', 0o666) 7 8 The returned object is a dbm.gnu, dbm.ndbm or dbm.dumb object, dependent on the 9 type of database being opened (determined by the whichdb function) in the case 10 of an existing dbm. If the dbm does not exist and the create or new flag ('c' 11 or 'n') was specified, the dbm type will be determined by the availability of 12 the modules (tested in the above order). 13 14 It has the following interface (key and data are strings): 15 16 d[key] = data # store data at key (may override data at 17 # existing key) 18 data = d[key] # retrieve data at key (raise KeyError if no 19 # such key) 20 del d[key] # delete data stored at key (raises KeyError 21 # if no such key) 22 flag = key in d # true if the key exists 23 list = d.keys() # return a list of all existing keys (slow!) 24 25 Future versions may change the order in which implementations are 26 tested for existence, and add interfaces to other dbm-like 27 implementations. 28 """ 29 30 __all__ = ['open', 'whichdb', 'error'] 31 32 import io 33 import os 34 import struct 35 import sys 36 37 38 class error(Exception): 39 pass 40 41 _names = ['dbm.gnu', 'dbm.ndbm', 'dbm.dumb'] 42 _defaultmod = None 43 _modules = {} 44 45 error = (error, OSError) 46 47 try: 48 from dbm import ndbm 49 except ImportError: 50 ndbm = None 51 52 53 def open(file, flag='r', mode=0o666): 54 """Open or create database at path given by *file*. 55 56 Optional argument *flag* can be 'r' (default) for read-only access, 'w' 57 for read-write access of an existing database, 'c' for read-write access 58 to a new or existing database, and 'n' for read-write access to a new 59 database. 60 61 Note: 'r' and 'w' fail if the database doesn't exist; 'c' creates it 62 only if it doesn't exist; and 'n' always creates a new database. 63 """ 64 global _defaultmod 65 if _defaultmod is None: 66 for name in _names: 67 try: 68 mod = __import__(name, fromlist=['open']) 69 except ImportError: 70 continue 71 if not _defaultmod: 72 _defaultmod = mod 73 _modules[name] = mod 74 if not _defaultmod: 75 raise ImportError("no dbm clone found; tried %s" % _names) 76 77 # guess the type of an existing database, if not creating a new one 78 result = whichdb(file) if 'n' not in flag else None 79 if result is None: 80 # db doesn't exist or 'n' flag was specified to create a new db 81 if 'c' in flag or 'n' in flag: 82 # file doesn't exist and the new flag was used so use default type 83 mod = _defaultmod 84 else: 85 raise error[0]("need 'c' or 'n' flag to open new db") 86 elif result == "": 87 # db type cannot be determined 88 raise error[0]("db type could not be determined") 89 elif result not in _modules: 90 raise error[0]("db type is {0}, but the module is not " 91 "available".format(result)) 92 else: 93 mod = _modules[result] 94 return mod.open(file, flag, mode) 95 96 97 def whichdb(filename): 98 """Guess which db package to use to open a db file. 99 100 Return values: 101 102 - None if the database file can't be read; 103 - empty string if the file can be read but can't be recognized 104 - the name of the dbm submodule (e.g. "ndbm" or "gnu") if recognized. 105 106 Importing the given module may still fail, and opening the 107 database using that module may still fail. 108 """ 109 110 # Check for ndbm first -- this has a .pag and a .dir file 111 try: 112 f = io.open(filename + ".pag", "rb") 113 f.close() 114 f = io.open(filename + ".dir", "rb") 115 f.close() 116 return "dbm.ndbm" 117 except OSError: 118 # some dbm emulations based on Berkeley DB generate a .db file 119 # some do not, but they should be caught by the bsd checks 120 try: 121 f = io.open(filename + ".db", "rb") 122 f.close() 123 # guarantee we can actually open the file using dbm 124 # kind of overkill, but since we are dealing with emulations 125 # it seems like a prudent step 126 if ndbm is not None: 127 d = ndbm.open(filename) 128 d.close() 129 return "dbm.ndbm" 130 except OSError: 131 pass 132 133 # Check for dumbdbm next -- this has a .dir and a .dat file 134 try: 135 # First check for presence of files 136 os.stat(filename + ".dat") 137 size = os.stat(filename + ".dir").st_size 138 # dumbdbm files with no keys are empty 139 if size == 0: 140 return "dbm.dumb" 141 f = io.open(filename + ".dir", "rb") 142 try: 143 if f.read(1) in (b"'", b'"'): 144 return "dbm.dumb" 145 finally: 146 f.close() 147 except OSError: 148 pass 149 150 # See if the file exists, return None if not 151 try: 152 f = io.open(filename, "rb") 153 except OSError: 154 return None 155 156 with f: 157 # Read the start of the file -- the magic number 158 s16 = f.read(16) 159 s = s16[0:4] 160 161 # Return "" if not at least 4 bytes 162 if len(s) != 4: 163 return "" 164 165 # Convert to 4-byte int in native byte order -- return "" if impossible 166 try: 167 (magic,) = struct.unpack("=l", s) 168 except struct.error: 169 return "" 170 171 # Check for GNU dbm 172 if magic in (0x13579ace, 0x13579acd, 0x13579acf): 173 return "dbm.gnu" 174 175 # Later versions of Berkeley db hash file have a 12-byte pad in 176 # front of the file type 177 try: 178 (magic,) = struct.unpack("=l", s16[-4:]) 179 except struct.error: 180 return "" 181 182 # Unknown 183 return "" 184 185 186 if __name__ == "__main__": 187 for filename in sys.argv[1:]: 188 print(whichdb(filename) or "UNKNOWN", filename) 189
